Injection devices

Abstract

An injection device has a two part barrel. The forward part (10) telescopes into the rear part (3) and within the barrel a capsule (1) with a needle (2) at its forward end is initially held by a trigger (11) formed integrally with the forward part (10) so that the needle (2) does not project. The trigger (11) is inoperable at this stage, being inaccessible because of the telescopic overlap. A spring (20) acts on a plunger at the rear of the capsule. When the overlap is increased, the trigger (11) becomes accessible through a slot (7), and when it is operated the capsule (1) is released for the spring (20) to shoot it forwards and eject the dose through the now projecting needle (2). The capsule (1) may have a two part dose and its mixing may then be effected by the spring (20), fully compressed after the overlap increase, urging the plunger forwards.

What is claimed is: 
     
       1. An injection device comprising a barrel (3, 10), spring means (20) within the barrel to act in a forward direction on a capsule (1) with a needle at its leading end housed therein, and a trigger (11) that holds the capsule (1) in a needle retracted position, actuation of the trigger (11) releasing the capsule for that to be urged forwardly by the spring means (20) to project the needle (2) through a passage at the leading end of the barrel (3, 10), characterised in that the trigger (11) has a portion for manual actuation and a portion (12, 14) that co-operates with the capsule, in that the barrel comprises two mutually telescoped parts (3, 10) one of which initially conceals said actuating portion, and in that, for operation, those parts have their telescopic overlap increased to energise the spring means (20) and to expose said portion for manual actuation. 
     
     
       2. An injection device as claimed in claim 1, characterised in that the spring means (20) are arranged, after urging the capsule (1) forwards, to have residual energy to act on the contents of the capsule to eject a dose through the needle (2). 
     
     
       3. An injection device as claimed in claim 1, characterised in that said forward part (10) telescopes into the rearward part (3). 
     
     
       4. An injection device as claimed in claim 1, characterised in that the trigger (11) is integrally formed with the part (10) that telescopes into the other part (3). 
     
     
       5. An injection device as claimed in claim 1, characterised in that there are detents (9, 15, 16) to resist the parts being detelescoped from the initial position and from the increased overlap position. 
     
     
       6. An injection device as claimed in claim 1, characterised in that the spring means (20) is a coil spring acting between the rear end (4) of the rearward barrel part (3) and the rear end of the capsule (1). 
     
     
       7. An injection device as claimed in claim 1, in combination with a capsule (1) containing two initially separate components, characterised in that a plunger at the rear end of the capsule is acted upon by the spring means (20), the increase in telescopic overlap causing the spring means to be compressed and subsequently re-expand to press the plunger forwards and thereby force one component in the capsule to mix with the other component. 
     
     
       8. An injection device as claimed in claim 7, characterized in that the spring means (20) are arranged, after urging the capsule (1) forwards, to have residual energy to act on the contents of the capsule to elect a dose through the needle (2) and that the travel of the plunger within the capsule during the mixing operation is less than the mutual movement of the two barrel parts when the overlap is increased, whereby the spring means (20) has residual energy after the components have been mixed, first, when the trigger is activated, to shoot the capsule (1) forwards to a limit, acting on the plunger, this projecting the needle (2), and then to press the plunger further into the capsule and thereby eject a dose through the needle (2). 
     
     
       9. An injection device as claimed in claim 1, in combination with a capsule, characterised in that the needle (2) is double-ended and there is a lost motion connection between means carrying the needle and the capsule (1) which is taken up during the forward movement of the capsule, causing the rear end of the needle to pierce a membrane defining the forward end of a dose chamber of the capsule.